Fan Dampers of Centrifugal Fan

ABSTRACT

A centrifugal fan is provided with an electric motor; an impeller driven by the electric motor; and fan dampers around an inner surface of fan housing and surrounding the impeller. Each fan damper has a windward, concave surface facing a rotational direction of the impeller. A spiral airflow created by the impeller passes the windward curved portions of the fan dampers and the motor toward an outlet. A portion of the kinetic energy of the spiral airflow is transmitted axially and the remaining kinetic energy of the spiral airflow is converted into static pressure to convey the spiral airflow toward the outlet so as to converge the spiral airflow from the electric motor to the outlet, thereby causing most of the spiral airflow to flow axially when it reaches the outlet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to centrifugal fans and more particularly to a centrifugal fan having improved fan dampers for effectively directing spiral airflow to axial airflow.

2. Description of Related Art

Typically, a mechanical fan can be classified as an axial type fan having a high volumetric flow rate and a centrifugal type fan (i.e., centrifugal fan) having a high static pressure. Centrifugal fans are particularly suitable to narrow outlet or complicated pipes. A centrifugal fan can be either a spiral air fan having an inlet and an outlet at angle of about 90-degree with respect to the inlet, or a linear air fan having an inlet, an impeller, and an outlet arranged in a straight line.

A typical centrifugal fan is shown in FIG. 1. Within an inlet housing 12, a hub of an impeller 13 is driven by a motor shaft of an electric motor 14. Thus, air is sucked into the inlet housing 12 via an inlet 10 and in turn the air is converted into a spiral air flow by the fan blades of the impeller 13. The spiral air flow presses against a diverging section 11 of an inner surface of the inlet housing 12 for diffusing so as to convert a portion of kinetic energy into static pressure. The static pressure further conveys the air flow forward to press against a convergent section 15 of an inner surface of an outlet housing 17. Finally, a great volume of pressurized air is outputted through an inlet 16.

However, only a portion of the kinetic energy is converted into static pressure by the diverging section 11 of the inner surface of the inlet housing 12. That is, a substantial portion of airflow is not directed to an axial direction before leaving the outlet 16.

Thus, the need for improvement still exists.

SUMMARY OF THE INVENTION

It is therefore one object of the invention to provide a centrifugal fan comprising an inlet housing including an axial inlet; an outlet housing including an axial outlet, the outlet housing being secured to the outlet housing to define an interior; an electric motor disposed in the interior; an impeller disposed in the interior and driven by the electric motor; and a plurality of fan dampers disposed around an inner surface of the interior and surrounding the impeller, each of the fan dampers having a windward, concave surface facing a rotational direction of the impeller; wherein a spiral airflow created by the impeller passes the windward curved portions of the fan dampers and the motor toward the outlet, and wherein a portion of the kinetic energy of the spiral airflow is transmitted axially and the remaining kinetic energy of the spiral airflow is converted into static pressure to convey the spiral airflow toward the outlet so as to converge the spiral airflow from the electric motor to the outlet, thereby causing most of the spiral airflow to flow axially when it reaches the outlet.

The above and other objects, features and advantages of the invention will become apparent from the following detailed description taken with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a broken away view of a typical centrifugal fan;

FIG. 2 is a perspective view of a centrifugal fan according to a first preferred embodiment of the invention;

FIG. 3 is an exploded view of the centrifugal fan shown in FIG. 2;

FIG. 4 is a sectional view of the centrifugal fan shown in FIG. 2;

FIG. 5 schematically depicts airflow through the impeller;

FIG. 6 is a chart showing airflow speed at the outlet and rotational speed of the impeller for the centrifugal fan of the first preferred embodiment of the invention having fan dampers and for a typical centrifugal fan without fan dampers;

FIG. 7 is a chart showing volumetric flow rate at the outlet and rotational speed of the impeller for the centrifugal fan of the first preferred embodiment of the invention having fan dampers and for a typical centrifugal fan without fan dampers;

FIG. 8 is a perspective view of a centrifugal fan according to a second preferred embodiment of the invention; and

FIG. 9 is a chart showing pressure in the combustion chamber and rotational speed of the impeller for the centrifugal fan of the second preferred embodiment of the invention having fan dampers and for a typical centrifugal fan without fan dampers.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 2 to 7, a centrifugal fan in accordance with a first preferred embodiment of the invention comprises the following components as discussed in detail below.

A bowl-shaped inlet housing 21 has a projecting inlet 20 at one end of its axis. A bowl-shaped outlet housing 25 has a projecting outlet 26 at one end of its axis. The inlet housing 21 and the outlet housing 25 are secured together to form a fan housing having an interior 27. An impeller 23 and an electric motor 24 are provided in the interior 27. A ring 28 is provided on an inner surface of the inlet housing 21 (or the outlet housing 25 in other embodiments). A plurality of equally spaced fan dampers 22 are formed on an inner surface of the ring 28 facing the impeller 23 surrounded by the ring 28. Each fan damper 22 has a windward, concave surface facing a rotational direction of the impeller 23.

The impeller 23 is driven by the motor 24 to create an airflow which pass curved surfaces of the fan dampers 22 and the motor 24 toward the outlet 26 in which a portion of the kinetic energy of the spiral airflow is transmitted axially and the remaining kinetic energy of the spiral airflow is converted into static pressure to convey the airflow toward the outlet 26. The airflow converges from the motor 24 to the outlet 26. As a result, most of the spiral airflow flows axially when it reaches the outlet 26.

Alternatively, the ring 28 is eliminated and the fan dampers 22 are formed integrally on an inner surface of the inlet housing 21 or the outlet housing 25 in other embodiments.

Still alternatively, the ring 28 is eliminated and the fan dampers 22 are manufactured separately prior to securing to an inner surface of the inlet housing 21 or the outlet housing 25 in other embodiments.

Preferably, the fan damper 22 is an elongated, curved plate having a smooth surface so that spiral airflow reaching its windward can be directed to flow axially after leaving its leeward. This has the benefit of increasing airflow along an axis of the centrifugal fan.

The fan damper 22 has a windward end 30 and a leeward end 32. The impeller 23 has a disc 31 with the fan blades equally spaced apart and formed proximate to an edge of one surface facing the inlet 20. The windward end 30 is at angle of 0-45 degrees with respect to the disc 31 in which the angle is increased axially. The leeward end 32 is at angle of 70-90 degrees with respect to the disc 31.

It is preferred that the greater of the angle between the windward end 30 and the disc 31 within a range the air control efficiency increases. Also, the greater of the angle between the leeward end 32 and the disc 31 within a range the air control efficiency increases. However, turbulence is created when the angle is greater than either range, and the turbulence can affect fan energy usage. An optimum angle can be obtained based on a rotational speed of the impeller 23. Practically, the angle can be increased for high speed impeller and the angle can be decreased for low speed impeller.

Referring to FIG. 6 specifically, it is a chart showing airflow speed at the outlet 26 and rotational speed of the impeller 23 for the centrifugal fan of the first preferred embodiment of invention having fan dampers 22 and for a typical centrifugal fan without fan dampers. As shown, the airflow speed at the outlet 26 increases about linearly as the rotational speed of the impeller 23 increases. Specifically, the airflow speed at the outlet is 13 m/s without the provision of fan dampers and the airflow speed at the outlet 26 is 18.2 m/s with the provision of fan dampers 22 when the rotational speed of the impeller 23 is 9,000 rpm (revolutions per minute). This means that the airflow speed at the outlet 26 increases by about 40% with the provision of the fan dampers 22 according to the first preferred embodiment of centrifugal fan of the invention.

Referring to FIG. 7 specifically, it is a chart showing volumetric flow rate at the outlet 26 and rotational speed of the impeller 23 for the centrifugal fan of the second preferred embodiment of invention having fan dampers 22 and for a typical centrifugal fan without fan dampers. As shown, the volumetric flow rate at the outlet 26 increases about linearly as the rotational speed of the impeller 23 increases. Specifically, the volumetric flow rate at the outlet is 0.0313 m³/s without the provision of fan dampers and the volumetric flow rate at the outlet 26 is 0.0441 m³/s with the provision of fan dampers 22 when the rotational speed of the impeller 23 is 9,000 rpm. This means that the volumetric flow rate at the outlet 26 increases by about 41% with the provision of the fan dampers 22 according to the second preferred embodiment of centrifugal fan of the invention.

Referring to FIGS. 8 and 9, a centrifugal fan in accordance with a second preferred embodiment of the invention is shown. The characteristics of the second preferred embodiment are substantially the same as that of the first preferred embodiment except the following:

The centrifugal fan is particularly used in a turbine engine. The centrifugal fan includes a fan housing 51, an impeller 52 disposed in an inlet of the fan housing 51, a starter motor (not shown) disposed in the fan housing 51, a combustion chamber 53 disposed in an intermediate portion of the fan housing 51, a turbine 54 disposed in an outlet of the fan housing 51, and a plurality of fan dampers 60 disposed proximate to an inner surface of the fan housing 51 and around leeway ends of fan blades of the impeller 52. The fan damper 60 is an elongated, curved plate having a smooth surface so that spiral airflow leaving the impeller 52 and reaching its windward can be directed to flow axially after leaving its leeward. It is noted that the fan damper 60 has a windward, concave surface facing a rotational direction of the impeller 52.

In operation, the impeller 52 is driven by the starter motor to create an airflow which passes curved surfaces of the fan dampers 60 toward the combustion chamber 53. Thus, pressure in the combustion chamber 53 increases. Fuel is injected into the combustion chamber 53 to mix with the pressurized air prior to combustion. The combusted mixture rotates the turbine 54 to generate mechanical energy in which a portion of the kinetic energy of the combusted mixture is used to rotate the impeller 52, thereby finishing a thermal cycle of the turbine engine.

The spiral airflow generated by the impeller 52 is converted into axial airflow and static pressure for increasing pressure in the combustion chamber 53. As a result, thermal efficiency of the turbine engine is increased.

Referring to FIG. 9 specifically, it is a chart showing pressure in the combustion chamber 53 and rotational speed of the impeller 52 for the centrifugal fan of the second preferred embodiment of the invention having fan dampers 60 and for a typical centrifugal fan without fan dampers. As shown, the pressure in the combustion chamber 53 increases about linearly as the rotational speed of the impeller 52 increases. Specifically, the pressure in the combustion chamber is 19.42 kpa without the provision of fan dampers and the pressure in the combustion chamber 53 is 24.87 kpa with the provision of fan dampers 60 when the rotational speed of the impeller 52 is 1.2 Mach. This means that pressure in the combustion chamber 53 increases by about 28% with the provision of the fan dampers 60 according to the second preferred embodiment of centrifugal fan of the invention.

While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims. 

What is claimed is:
 1. A centrifugal fan comprising: an inlet housing including an axial inlet; an outlet housing including an axial outlet, the outlet housing being secured to the outlet housing to define an interior; an electric motor disposed in the interior; an impeller disposed in the interior and driven by the electric motor; and a plurality of fan dampers disposed around an inner surface of the interior and surrounding the impeller, each of the fan dampers having a windward, concave surface facing a rotational direction of the impeller; wherein a spiral airflow created by the impeller passes the windward curved portions of the fan dampers and the motor toward the outlet, and wherein a portion of the kinetic energy of the spiral airflow is transmitted axially and the remaining kinetic energy of the spiral airflow is converted into static pressure to convey the spiral airflow toward the outlet so as to converge the spiral airflow from the electric motor to the outlet, thereby causing most of the spiral airflow to flow axially when it reaches the outlet.
 2. The centrifugal fan of claim 1, wherein the fan dampers are formed integrally with the inlet housing or the outlet housing.
 3. The centrifugal fan of claim 1, wherein the fan dampers are manufactured separately prior to securing to an inner surface of the inlet housing or the outlet housing.
 4. The centrifugal fan of claim 1, wherein each of the fan damper has a windward end and a leeward end, wherein the impeller has a disc, wherein the windward end is at angle of 0-45 degrees with respect to the disc with the angle being increased axially, and wherein the leeward end is at angle of 70-90 degrees with respect to the disc.
 5. A centrifugal fan comprising: a fan housing; an impeller disposed in a forward end of the fan housing; a starter motor disposed adjacent to the impeller in the fan housing; a combustion chamber disposed in an intermediate portion of the fan housing; a turbine disposed in a rear end of the fan housing; and a plurality of fan dampers disposed proximate to an inner surface of the fan housing and around the impeller, each of the fan dampers having a windward, concave surface facing a rotational direction of the impeller; wherein a spiral airflow created by the impeller passes the windward curved portions of the fan dampers toward the combustion chamber, wherein a portion of the kinetic energy of the spiral airflow is transmitted axially and the remaining kinetic energy of the spiral airflow is converted into static pressure to convey the spiral airflow toward the combustion chamber, wherein fuel is injected into the combustion chamber to mix with air prior to combustion, and wherein the combusted mixture rotates the turbine to generate mechanical energy. 